By combining two separate quantum simulation approaches—density functional theory and quantum Monte Carlo—a team of physicists, including David Ceperley and Miguel Morales at the University of Illinois, have discovered a first-order phase transition in liquid hydrogen between a molecular state having low electrical conductivity and a highly conductive atomic state. The discontinuity is predicted to occur at very high temperatures (near 2000 K) and pressures (near 120 GPa). Their results were reported in the June 28 Proc. Natl. Acad. Sci.
"Our simulations showed that the electrical conductivity of liquid hydrogen increases discontinuously in a range of densities at temperatures below 2000 K," said Miguel Morales (now at Rice University). "A liquid-liquid-solid multiphase coexists at a point in the hydrogen phase diagram where the liquid-liquid phase transition intersects the melting line of the molecular solid."
Hydrogen, the most abundant element in the universe, comprises most of the mass of giant planets, such as Jupiter and Saturn. Understanding the onset of molecular disassociation in hydrogen under high pressure may shed light on the formation of these planets.
Besides Morales and Ceperley, the collaboration included Eric Schwegler (Lawrence Livermore National Laboratory) and Carlo Pierleoni (University of L'Aquila). The work was funded in part by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program.